Method and apparatus for tracking error detection in optical disk driver

ABSTRACT

A method and apparatus for tracking error detection in an optical disk reproduction system. The tracking error detecting apparatus generates a tracking error signal as a difference signal of optical detection signals generated by more than two optical detectors positioned along a diagonal line from a track center and includes binarizers which binarize each output of the optical detectors, phase locked loops (PLLs) which generate respective clock signals synchronized with the outputs of each of the binarizers, a phase difference detector which detects a phase difference between the synchronized signals output from the PLLs, and low-pass filters which filter the output of the phase difference detector to output the result as the tracking error signal. The tracking error detecting apparatus generates a tracking error signal which is not dependent on the lengths of pits or marks recorded on an optical disk, enhancing the reliability of the tracking error signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/613,695, filed Jul. 10, 2000, now pending, which claims the benefitof Korean Application No. 99-27451, filed Jul. 8, 1999, in the KoreanPatent Office, the disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for trackingerror detection and more particularly, to an improved method andapparatus for tracking error detection in which a phase locked loop(PLL) is introduced into a conventional differential phase detectiontracking error (DPD TE) method to increase the accuracy of trackingerror detection.

2. Description of the Related Art

In a conventional DPD TE method, phase differences are generated on theedges of pits or marks of an optical disk. The length of pits or marksrecorded on an optical disk lies in various ranges. For example, in thecase of digital versatile disk-ROM (DVD-ROM), a length ranges from 3T to14T where T is the duration of a channel clock of the disk. If there area lot of pits or marks having a short length, phase difference detectioncan be performed many times, thereby enhancing the reliability of atracking error signal derived therefrom. Conversely, if there are morepits or marks having a long length, the number of times phase differencedetection may be done is reduced, thereby degrading the reliability of atracking error signal. Further, a spectrum component, according to amodulation method of signal recorded on a disk, is closely related tooutputs of AC+ and BD+, and a low-frequency component of the spectrumacts on noise with regard to a tracking error signal which is used forfollowing and determining the position of a tracking center.

According to a conventional DPD TE method, phase difference detection issupposed to be made from pits or marks at one time, so that the gain andcharacteristics of a detected signal deteriorate if the signal of pitsor marks is adversely affected by defects or the like. In addition, asthe track density of an optical disk increases, the magnitude and gainof a tracking error signal according to the conventional DPD TE methoddecrease. Thus, the conventional DPD TE method has a disadvantage inthat it is difficult to precisely control tracking in a high-densitytrack structure. Referring to FIG. 1, the configuration of a trackingerror detecting apparatus according to a conventional differential phasedetection tracking error (DPD TE) method is shown. The apparatus shownin FIG. 1 includes a four-section optical detection unit 102, a matrixcircuit 104, high-pass filters (HPFs) 106 a and 106 b, comparators 108 aand 108 b, a phase comparator 110, and a low-pass filter (LPF) 112. Theapparatus detects a phase difference between the signals output from thefour-section optical detection unit 102 to determine the position of alaser spot. If the laser spot deviates from a track center, then a timedelay or a phase difference between A+C and B+D signals results. Thus, atracking error signal is generated by detecting the time delay betweenthose signals.

Specifically, the matrix circuit 104 adds optical detection signals Aand B, and C and D, which are positioned along a diagonal line among theoutputs (A, B, C and D) of the four-section optical detection unit 102,and outputs AC1 and BD1 from A+C and B+D, respectively. The HPFs 106 aand 106 b reinforce the high-frequency components of AC1 and BD1provided from the matrix circuit 104, differentiate AC1 and BD1, andoutput the results, i.e., AC2 and BD2 to the comparators 108 a and 108b. The comparators 108 a and 108 b binarize each of AC2 and BD2 providedfrom the HPFs 106 a and 106 b, compare AC2 and BD2 with a predeterminedlevel (a ground level in FIG. 1) to output the results, i.e., AC3 andBD3 to the phase comparator 110.

The phase comparator 110 detects a phase difference between AC3 and BD3provided from the comparators 108 a and 108 b, compares the phases ofAC3 and BD3 to output the results, i.e., AC+ and BD+ to the LPF 112. Inthis case, AC+ is a phase difference signal generated when AC3 leads BD3in phase, while BD+ is a phase difference signal generated when BD3leads AC3 in phase. The LPF 112 filters AC+ and BD+ input from the phasecomparator 110 and outputs the result as a tracking error signal.

FIGS. 2A-2D are waveform diagrams illustrating operation of theapparatus shown in FIG. 1. FIGS. 2A-2D show the case in which AC3 leadsBD3 in phase. The wave forms of AC3, BD3, AC+ and BD+ signals areillustrated sequentially from FIG. 2A to FIG. 2D. As shown in FIGS.2A-2D, it can be found that if a laser spot deviates by a predeterminedamount, there exists a phase difference between AC3 and BD3, shown inFIG. 2A and FIG. 2B, respectively, which is in turn reflected into AC+and BD+, shown in FIG. 2C and FIG. 2D, respectively. If AC3 leads BD3 inphase, a tracking error signal is greater than a predetermined centralvalue, but in the opposite case, it is less than the predeterminedcentral value. The degree to which a tracking error signal deviates fromthe central value corresponds to the distance by which the laser spot isdeparted from the track center.

The phase comparator 110 of the apparatus shown in FIG. 1 detects aphase difference at a rising or falling edge of AC3 and BD3. The risingor falling edges of AC3 and BD3 correspond to the edges of pits or marksrecorded on an optical disk. In other words, the apparatus shown in FIG.1 detects a phase difference once on every edge of pits and marksrecorded on an optical disk. Thus, as the number of pits or marksincreases, the reliability of a tracking error signal increases, and asthe number of pits or marks decreases, the reliability of the signaldecreases. If pits or marks are affected by defects of an optical diskor other factors, the gain and characteristics of a tracking errorsignal become worse. A spectrum component according to a recordingmodulation method is closely connected with AC+ and BD+, and especiallya low-frequency component of the spectrum works on noise with regard toa tracking error signal. Further, in the case of a tracking error signalaccording to the DPD TE method, the magnitude and gain are reduced astrack density is increased, which makes the accurate control of trackingin a high track- density structure difficult.

SUMMARY OF THE INVENTION

In order to improve such drawbacks, a tracking error detecting methodaccording to the present invention involves generating clock signals,synchronized with each of the binarized signals AC3 and BD3, to detect aphase difference between those clock signals. In this case, all pulsesin the synchronized clock signals have the phase difference componentsof AC+ and BD+, so that a tracking error signal can be generatedregardless of the lengths of pits or marks recorded on a disk.

In the present invention, outputs of optical detectors which aredisposed along a diagonal line from a track center are each binarized.Clock signals synchronized with each of the outputs obtained from thebinarization are generated by Phase Locked Loop (PLL) circuits. When alaser spot deviates from a track center, the outputs AC3 and BD3obtained from the binarization have a phase difference corresponding tothe deviation degree of the laser spot with regard to the track center,and the clocks which are phase locked to the outputs have the same phasedifference. A phase difference between the synchronized clock signalsoutput in the phase locking is detected. All clocks in the synchronizedclock signals have the phase difference components of AC+ and BD+, sothat a phase difference component is detected on a clock-by-clock basis.The output from the phase difference detection is filtered by an LPF toobtain a tracking error signal.

It is an object of the present invention to provide a method ofimproving the accuracy of a tracking error detection with theintroduction of a phase locked loop (PLL) into a conventionaldifferential phase detection tracking error (DPD TE) method.

It is another object of the present invention to provide an apparatususing the above method.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

Accordingly, to achieve one object of the invention, there is provided atracking error detecting method for producing a tracking error signal asa difference signal between optical detection signals generated frommore than two optical detectors which are positioned along a diagonalline from a track center. The method according to the present inventionincludes binarizing the outputs of the optical detectors, phase-lockingto generate clock signals synchronized with each of the outputs obtainedfrom the binarization, detecting phase differences between thesynchronized clock signals output from the phase-locking, and low-passfiltering the output of the phase difference detection, to output thetracking error signal.

In order to achieve another object, the present invention provides afirst embodiment of a tracking error detection apparatus for producing atracking error signal based on a difference signal of optical detectionsignals generated from more than two optical detectors which arepositioned along a diagonal line from a track center. The firstpreferred embodiment of the apparatus according to the present inventionincludes binarizers which binarize each of the outputs of the opticaldetectors, PLLs which generate clock signals synchronized with each ofthe outputs of the binarizers, a phase difference detector which detectsa phase difference between the synchronized clock signals output fromthe PLLs, and a low-pass filter which filters the output of the phasedifference detector to output the result as the tracking error signal.In this case, it is preferable to further include a frequency dividerfor dividing the frequency of a channel clock signal by n (n=2,3,4, . .. ) to output the signal to the PLLs in the event that the phase of anoutput signal is inverted.

In order to achieve another object, the present invention also providesa second embodiment of a tracking error detecting apparatus forproducing a tracking error signal based on a difference signal ofoptical detection signals generated from two optical detectors disposedat the outside of the track center of a three-section optical detectionunit. The second preferred embodiment of the apparatus according to thepresent invention includes binarizers which binarize each of the outputsof the optical detectors, a phase difference detector which detects aphase difference between the outputs of the binarizers, and a low-passfilter which filters the output of the phase difference detector tooutput the result as a tracking error signal. In this case, it ispreferable that the tracking error detecting apparatus further includesPLLs coupled to the binarizers and to the phase difference detector, inorder to generate clock signals synchronized with each of the outputs ofthe binarizers and to output the synchronized clock signals to the phasedifference detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objectives and advantages of the present invention will becomemore apparent by describing in detail preferred embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a block diagram of a tracking error detecting apparatusaccording to a conventional differential phase detection tracking error(DPD TE) method;

FIGS. 2A-2D are waveform diagrams showing the operation of the apparatusshown in FIG. 1;

FIG. 3 is a block diagram of a first preferred embodiment of a trackingerror detecting apparatus according to the present invention;

FIGS. 4A-4F are waveform diagrams showing the operation of the apparatusshown in FIG. 3;

FIG. 5 is a block diagram of a second preferred embodiment of a trackingerror detecting apparatus according to the present invention;

FIG. 6 is a block diagram of a third preferred embodiment of a trackingerror detecting apparatus according to the present invention;

FIG. 7 is a block diagram of a fourth preferred embodiment of a trackingerror detecting apparatus according to the present invention;

FIG. 8 is a graph of gain versus frequency for the equalizers shown inFIGS. 3 and 5-7;

FIG. 9 is a graph showing the result of comparing a tracking errorsignal generated by a tracking error detecting apparatus according tothe present invention, with a tracking signal generated by aconventional DPD TE method; and

FIG. 10 is a graph showing the characteristic of gain of tracking errorsignals generated by a tracking error detecting apparatus according tothe present invention and a conventional DPD TE method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings, where like reference numerals refer tolike elements throughout.

FIG. 3 is a block diagram showing a first preferred embodiment of atracking error detecting apparatus according to the present invention.The apparatus shown in FIG. 3 includes a four-section optical detectionunit 302, a matrix circuit 304, equalizers (EQs) 306 a and 306 b,binarizers 308 a and 308 b, PLLs 310 a and 310 b, a phase comparator312, LPFs 314 a and 314 b, a differential amplifier 316, and a frequencydivider 318.

The matrix circuit 304 adds optical detection signals A and C, and B andD among the outputs A, B, C and D of the four-section optical detectionunit 302, and outputs AC1 and BD1 corresponding to A+C and B+D,respectively. That is, the matrix circuit 304 produces summation signalsof the signals generated by optical detectors which are positioned alonga diagonal line from a track center. The EQs 306 a and 306 b strengthenthe high-frequency components of AC1 and BD1 provided from the matrixcircuit 304 and remove noise therefrom, differentiate AC1 and BD1 andremove noise therefrom to output the results AC2 and BD2 to thebinarizers 308 a and 308 b. In other words, since the outputs A, B, Cand D of the four-section optical detection unit 302 have weakhigh-frequency components, the high-frequency components of AC1 and BD1provided from the matrix circuit 304 are reinforced through the EQs 306a and 306 b. Further, as the outputs A, B, C and D of the four-sectionoptical detection unit 302 contain a noise component in addition tosignals reflected from an optical disk, EQs 306 a and 306 b eliminatethe noise component in AC1 and BD1 provided from the matrix circuit 304.

The binarizers 308 a and 308 b convert AC2 and BD2 provided from EQs 306a and 306 b into binary digital signals and output the results AC3 andBD3 to the PLLs 310 a and 310 b. Binarizers 308 a and 308 b also performbinarization level compensation for AC2 and BD2 provided from the EQs306 a and 306 b. The PLLs 310 a and 310 b accept the input signals CLK,AC3 and BD3 and output CLK_AC and CLK_BD, synchronized with AC3 and BD3,respectively, to the phase comparator 312. The phase comparator 312detects a phase difference between CLK_AC and CLK_BD, and compares thephases of CLK_AC and CLK_BD to output the results AC+ and BD+ to LPFs314 a and 314 b, respectively. In this case, AC+ and BD+ are phasedifference signals generated when CLK_AC leads CLK_BD in phase and whenCLK_BD leads CLK_AC in phase, respectively.

The LPFs 314 a and 314 b filter AC+ and BD+ provided from the phasecomparator 312 to output the results to the differential amplifier 316.The differential amplifier 316 amplifies the difference signal of AC+and BD+ filtered by the LPFs 314 a and 314 b to output the result as atracking error signal (TE).

FIGS. 4A-4F are waveform diagrams showing the operation of the apparatusshown in FIG. 3. FIGS. 4A-4F show the case in which AC3 leads BD3 inphase, the wave forms of AC3, BD3, CLK_AC, CLK_BD, AC+, and BD+ signalsare illustrated sequentially in FIGS. 4A-4F, respectively. As shown inFIGS. 4A-4F, it can be found that if a laser spot deviates from a trackcenter by a predetermined amount, a phase difference existing betweenAC3 and BD3 is transferred to CLK_AC and CLK_BD, doubling by a CLKfrequency. FIGS. 4A-4F indicate that CLK_AC and CLK_BD synchronized withAC3 and BD3 respectively are generated and a phase difference At createdbetween AC3 and BD3 is transferred to the outputs CLK_AC and CLK_BD ofthe PLLs 310 a and 310 b. Thus, the phase difference value Δt is derivedas a result of comparing the phases of CLK_AC and CLK_BD.

The conventional apparatus shown in FIG. 1 detects the phase differenceΔt once in an interval t1 as shown in FIG. 2A-2D, while the apparatusaccording to the present invention can detect the phase difference Δtonce every cycle of CLKs. When a channel clock is used as CLK, the phasedifference Δt can be detected once every channel clock cycle Tregardless of the lengths of pits or marks recorded on an optical disk.The frequency divider 318 frequency divides CLK at an interval whereinversion of the output signal takes place, to output the result to thePLLs 310 a and 310 b. Inversion of the output signal occurs when thephase difference of a clock provided to the AC3 and the PLL 310 a or aclock provided to the BD3 and the PLL 310 b is beyond a detection rangeof the PLL 310 a and 310 b. Divider 318 detects whether the outputsignal TE OUT has been inverted and performs a division operation whenthe output signal TE OUT is inverted as in the interval 93 of FIG. 9.Alternately, divider 318 detects the output signals of PLLs 310 a and310 b to determine whether TE OUT has been inverted. In the apparatus ofFIG. 3, a tracking servo control becomes unstable at the interval whereinversion of the output signal happens. This is because inversion of theoutput signals causes deviation from the extent of phase differencedetection by the PLLs 310 a and 310 b. Thus, in order to compensate forthe deviation, the frequency of CLK is divided at the interval whereinversion of the output signal occurs and the result is provided to thePLLs 310 a and 310 b.

FIG. 5 is a block diagram showing a second embodiment of a trackingerror detecting apparatus according to the present invention. Theapparatus shown in FIG. 5 includes a four-section optical detection unit502, EQs 506 a-506 d, binarizers 508 a-508 d, PLLs 510 a-510 d, phasecomparators 512 a and 512 b, LPFs 514 a-514 d, differential amplifiers516 a and 516 b, and an adder 518. Since outputs A, B, C and D of thefour-section optical detection unit 502 have weak high-frequencycomponents, a high-frequency component of A, B, C and D provided fromthe four-section optical detection unit 502 is reinforced through theEQs 506 a-506 d. Further, as the outputs A, B, C and D of thefour-section optical detection unit 502 contain noise in addition tosignals reflected from an optical disk, EQs 506 a-506 d eliminate thenoise components of A, B, C and D provided from the four-section opticaldetection unit 502.

The binarizers 508 a-508 d convert signals provided from EQs 506 a-506 binto binary digital signals to output the results to the PLLs 510 a-510d. The PLLs 510 a-510 d receive as input the signal CLK and the signalsprovided from the binarizers 508 a-508 d to output CLKs, CLK_A, CLK_B,CLK_C and CLK_D, synchronized with the signals provided from thebinarizers 508 a-508 d to the phase comparators 512 a and 512 b. Thephase comparators 512 a and 512 b detect phase differences between CLK_Aand CLK_B and between CLK_C and CLK_D provided from the PLLs 510 a-510d. The phase comparator 512 a compares the phases of CLK_A and CLK_B tooutput the results A+ and B+ to the LPFs 514 a and 514 b, respectively,while the phase comparator 512 b compares the phases of CLK_C and CLK_Dto output the results C+ and D+ to the LPFs 514 c and 514 d,respectively. In this case, A+ and B+ are phase difference signalsgenerated when CLK_A leads CLK_B in phase and when CLK_B leads CLK_A inphase, respectively. Further, C+ and D+ are phase difference signalsgenerated when CLK_C leads CLK_D in phase and when CLK_D leads CLK_C inphase, respectively.

The LPFs 514 a-514 d filter A+, B+, C+ and D+ provided from the phasecomparators 512 a and 512 b to output the results to the differentialamplifiers 516 a and 516 b. The differential amplifiers 516 a and 516 bamplify the difference signals of A+ and B+, and C+ and D+ filtered bythe LPFs 514 a to 514 d to output the results to the adder 518. Theadder 518 adds the signals provided from the differential amplifiers 516a and 516 b to output the result as TE.

FIG. 6 is a block diagram showing a third preferred embodiment of atracking error detecting apparatus according to the present invention,in which TE is produced using outputs of a three-section opticaldetection unit. The apparatus shown in FIG. 6 includes a three-sectionoptical detection unit 602, EQs 606 a and 606 b, binarizers 608 a and608 b, PLLs 610 a and 610 b, a phase comparator 612, LPFs 614 a and 614b, and a differential amplifier 616.

The detection unit 602 has three optical detectors which are arrangedtransverse to a tangential direction of the recording track. The opticaldetectors generate electrical signals E, F and G corresponding to lightreflected from the recording track. The EQs 606 a and 606 b strengthenthe high-frequency components of signals E and G provided from opticaldetectors disposed at the outside of the three-section optical detectionunit 602 and remove noise therefrom, differentiate E and G and removenoise therefrom to output the results to the binarizers 608 a and 608 b.The binarizers 608 a and 608 b convert the signals provided from EQs 606a and 606 b into binary digital signals to output the results E3 and G3to the PLLs 610 a and 610 b, respectively. The PLLs 610 a and 610 breceive as input CLK, E3 and G3 to output CLK_E and CLK_G synchronizedwith E3 and G3 to the phase comparator 612. The phase comparator 612compares the phases of CLK_E and CLK_G arid outputs the results E+ andG+ to the LPFs 614 a and 614 b, respectively. In this case, E+ and G+are phase difference signals generated when CLK_E leads CLK_G in phaseand when CLK_G leads CLK_E in phase, respectively.

The LPFs 614 a and 614 b filter E+ and G+ provided from the phasecomparator 612 to output the results to the differential amplifier 616.The differential amplifier 616 amplifies the difference signal of E+ andG+ filtered by the LPFs 614 a and 614 b to output the result as TE.

FIG. 7 is a block diagram showing a fourth preferred embodiment of atracking error detecting apparatus according to the present invention inwhich TE is produced using the output of a three-section opticaldetection unit. The apparatus shown in FIG. 7 includes a three-sectionoptical detection unit 702, EQs 706 a and 706 b, binarizers 708 a and708 b, a phase comparator 712, LPFs 714 a and 714 b, and a differentialamplifier 716.

The detection unit 702 has three optical detectors which are arrangedtransverse to a tangential direction of the recording track. The opticaldetectors generate electrical signals E, F and G corresponding to lightreflected from the recording track. The EQs 706 a and 706 bdifferentiate E and G and remove noise therefrom to strengthen the highfrequency component of signals E and G and output the results to thebinarizers 708 a and 708 b. The binarizers 708 a and 708 b binarize thesignals provided from EQs 706 a and 706 b into binary digital signals tooutput the results E3 and G3 to the phase comparator 712. The phasecomparator 712 compares the phases of E3 and G3 to output the results E+and G+ to the LPFs 714 a and 714 b, respectively. In this case, E+ andG+ are phase difference signals generated when E3 leads G3 in phase andwhen G3 leads E3 in phase, respectively.

The LPFs 714 a and 714 b filter E+ and G+ provided from the phasecomparator 712 to output the results to the differential amplifier 716.The differential amplifier 716 amplifies the difference signal of E+ andG+ filtered by the LPFs 714 a and 714 b to output the result as TE.

FIG. 8 is a graph showing operation of the EQs of FIGS. 3 and 5-7, inwhich the vertical axis and the horizontal axis indicate gain andfrequency, respectively. The EQs, having the properties as shown in FIG.8, perform the function of controlling their properties so that an inputsignal can be positioned between a first frequency f1 and a secondfrequency f2 to amplify the high-frequency component which is close tothe second frequency f2.

FIG. 9 is a graph showing the result of comparing a tracking errorsignal generated by a tracking error detecting apparatus according tothe present invention with a tracking signal generated by a conventionalDPD TE method. In FIG. 9, reference numerals 91 and 92 respectivelyrepresent tracking error signals generated by a conventional DPD TEmethod and a tracking error detecting apparatus according to the presentinvention, and it can be seen that the gain of the latter is greaterthan that of the former. Further, an interval 93 indicates the sectionwhere inversion of output signal occurs so that a phase difference willexceed the detection limit if the phase difference is detected using theCLKs generated from the PLLs as in the present invention. If this is thecase, the frequency of the PLL CLK is divided by n (n=2,3,4, . . . ) andthe result is output to a phase difference detector, which increases thedetection extent so that intervals such as 93 will not exist.

FIG. 10 is a graph showing the characteristic of gain of tracking errorsignals generated by a tracking error detecting apparatus according tothe present invention and a conventional DPD TE method. In FIG. 10,reference numerals 94 and 95 respectively indicate the gains of trackingerror signals generated by the conventional DPD TE method and thetracking error detecting apparatus according to the present invention.If both are measured under the same conditions, it can be seen that thegain of a tracking error signal generated in the apparatus according tothe present invention is about 10 times greater than the gain of theother. An interval 96 is the section where an optical pickup jumps on anadjacent track in a normal tracking state. While the interval 96 cannotbe shown clearly in a tracking error signal generated by theconventional DPD TE method, it is output as a large value in a trackingerror signal generated by the present invention.

As described in the foregoing, a tracking error detecting apparatusaccording to the present invention is capable of generating a trackingerror signal which does not vary depending on the lengths of pits andmarks recorded on a optical disk, so that reliability of the trackingerror signal can be enhanced.

Although a few preferred embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

1. A method of producing a tracking error signal as a difference signalof optical detection signals generated by more than two opticaldetectors positioned along a line diagonal to a track center, the methodcomprising: binarizing each of the outputs of the optical detectors;phase locking to generate respective clock signals synchronized witheach of the binarized outputs; detecting a phase difference between thesynchronized clock signals; and low-pass filtering the detected phasedifference to output the tracking error signal. 2-17. (canceled)
 18. Themethod of claim 1, wherein the phase locking comprises generating afirst clock signal and phase locking each of the outputs of the opticaldetectors with the first clock signal to generate the respective clocksignals.
 19. The method of claim 18, further comprising: dividing thefirst clock signal when the output tracking error signal is invertedaccording to the first clock signal being outside the range of the phaselocking.
 20. The method of claim 1, further comprising: amplifying thebinarized outputs to improve a signal to noise ratio.
 21. A method ofproducing a tracking error signal for a disc in an optical recordingand/or reproducing apparatus, comprising: generating detection signalsfrom a plurality of optical detectors disposed transverse to atangential direction of a recording track of the disc; binarizing thedetection signals generated by a first one of the plurality of opticaldetectors disposed at a first end and a second one of the plurality ofoptical detectors disposed at a second end opposite the first end; phaselocking the binarized detection signals to a clock signal; comparingphases of the locked detection signals to generate phase differencesignals according to which of the locked detection signals is leading;and adding the generated phase difference signals to generate thetracking error signal.
 22. The method of claim 21, further comprising:dividing the clock signal when the generated tracking error signal isinverted at a frequency interval where the inversion occurs.
 23. Themethod of claim 21, further comprising: amplifying the binarizeddetection signals to improve a signal to noise ratio.
 24. A method ofproducing a tracking error signal for an optical recording medium, themethod comprising: generating first and second detection signals bybinarizing optical reflection signals in a track direction of theoptical recording medium; locking the first and second detection signalsto a clock signal to generate locked first and second detection signals;detecting a phase difference between the first and second lockeddetection signals once every cycle of the clock signal; and generatingthe tracking error signal for the optical recording medium according tothe detected phase difference.
 25. The method of claim 24, furthercomprising: dividing the clock signal when the generated tracking errorsignal is inverted at a frequency interval where the inversion occurs.26. The method of claim 25, wherein the clock signal is divided by nuntil the tracking error signal is no longer inverted, where n is apositive whole number greater than or equal to
 2. 27. The method ofclaim 24, further comprising: amplifying the first and second detectionsignals to improve a signal to noise ratio.
 28. The method of claim 24,wherein the generating the first and second detection signals comprisesbinarizing a first one of the optical reflection signals and a secondone of the optical reflection signals at opposite ends of a three unitphotodetector.